In the following description, carriers are schematically explained.
First of all, a user is able to provide information to transmit by modulating and manipulating an amplitude, frequency and/or phase of a sinusoidal wave or a periodic pulse wave. In this case, the sinusoidal or periodic pulse wave playing a role in carrying the information is called a carrier.
Carrier modulation schemes may be classified into a single-carrier modulation (SCM) scheme and a multicarrier modulation (MCM) scheme. In particular, the single-carrier modulation (SCM) scheme is a modulation scheme of having all information carried on a single carrier.
According to the multicarrier modulation (MCM) scheme, a whole bandwidth channel of a single carrier is divided into a plurality of subchannels having small bandwidths and a plurality of narrowband subcarriers are transmitted on the subchannels by multiplexing.
In doing so, if the multicarrier modulation (MCM) scheme is used, a plurality of the subchannels may be approximated to a flat channel owing to their small bandwidths. And, a user may be able to compensate for channel distortion using a simple equalizer. Moreover, the multicarrier modulation (MCM) scheme enables fast implementation using Fast Fourier Transform (FFT). In particular, the multicarrier modulation (MCM) scheme is superior to the single-carrier modulation (SCM) scheme in aspect of fast data transmission.
As the performance of a base station and/or a mobile station is being increasingly enhanced, a frequency bandwidth providable or available for the base station and/or the mobile station is extending increasingly. Hence, according to embodiments of the present invention, a multicarrier system supportive of a broadband in a manner of aggregating at least one or more carriers together is disclosed.
In particular, a multicarrier system mentioned in the following description corresponds to a case of aggregating at least one or more carriers to use, which is different from the above-mentioned multicarrier modulation (MCM) scheme of dividing a single carrier to use.
In order to efficiently use multi-band or multicarrier, a scheme for a single medium access control (MAC) entity to manage several carriers (e.g., several frequency carriers (FCs)) has been proposed.
FIG. 1 (a) and FIG. 1 (b) are diagrams to describe a multi-band radio frequency (RF) based signal transceiving method.
Referring to FIG. 1, a medium access control (MAC) layer in a transmitting/receiving side may be able to manage a plurality of carriers to efficiently use multiple carriers. In doing so, in order to effectively transceive multiple carriers, assume that both of the transmitting side and the receiving side are capable of transceiving the multiple carriers. In this case, since it is unnecessary for frequency carriers (FCs) managed by the MAC layer to be contiguous with each other, it is flexible in aspect of resource management. In particular, both contiguous carrier aggregation and non-contiguous carrier aggregation are possible.
Referring to FIG. 1 (a) and FIG. 1 (b), physical layers PHY 0 to PHY n−1 indicate multiple bands of the present invention, respectively. Each of the multiple bands may have a frequency carrier (FC) size assigned to a specific service by a previously determined frequency policy. For instance, PHY 0 (RF carrier 0) may have a size of a frequency band assigned for a normal FM radio broadcast and PHY 1 (RF carrier 1) may have a size of a frequency band assigned for a mobile phone communication.
Thus, the respective frequency bands may differ from each other in frequency band size in accordance with frequency band properties, respectively. For clarity, in the following description, assume that each frequency carrier (FC) has a size of A MHz. And, each of the frequency assignment brands may be represented as a carrier frequency to use a baseband signal on a corresponding frequency band. In the following description, each frequency assignment band shall be named a carrier frequency band. If here is no confusion, each carrier frequency band shall be simply named a carrier. Moreover, as recently defined in 3GPP LTE-A, the above-mentioned carrier may be called a component carrier to be discriminated from a subcarrier used by a multicarrier system.
In this aspect, the multi-band scheme may be called a multicarrier scheme or a carrier aggregation scheme.
FIG. 2 a diagram for one example of illustrating how multiple carriers are used in a general wireless communication system.
Referring to FIG. 2, a multicarrier in a general technology may include contiguous carrier aggregation [FIG. 2 (a)] or non-contiguous carrier aggregation [FIG. 2 (b)]. In this case, a unit of the carrier aggregation is a basic bandwidth unit of a general legacy system (e.g., LTE in case of LTE-A (long term evolution-advanced) system, IEEE 802.16e in case of IEEE 802.16m system). In a multicarrier configuration of a general technology, carriers of two types are defined as follows.
First of all, a 1st carrier (or, a primary carrier) means a carrier means a carrier for exchanging traffics and full PHY/MAC control information between a mobile station and a base station. And, the primary carrier may be usable for such a general operation of a mobile station as a network entry and the like. Moreover, each mobile station has one primary carrier in one cell.
Secondly, a 2nd carrier (or, a secondary carrier) generally means a supplementary carrier usable for an exchange of traffics in accordance with a MS-specific assignment command and rule received on the 1st carrier. The 2nd carrier may include control signaling to support a multicarrier operation. Generally, all control informations and information on a secondary information are received via a primary carrier and data is transmitted and received on the secondary carrier.
General technology may be able to categorize carriers of a multicarrier system into a fully configured carrier and a partially configured carrier based on the above-described primary and secondary carriers.
First of all, the fully configured carrier may indicate the carrier for configuring all control signals including synchronization, broadcast, multicast and unicast control channels. Moreover, informations and parameters for carriers different from those of the multicarrier operation may be included in the control channels.
Secondly, the partially configured carrier may mean the carrier for configuring all control channels to support a DL transmission in a DL carrier having no UL carrier to pair in a TDD (time division duplex) DL transmission or FDD (frequency division duplex) mode. A secondary carrier, which is a fully configured carrier configured in a prescribed mobile station may be allocated as a primary carrier of another mobile station.
Generally, a mobile station performs an initial network entry via a primary carrier and may be able to exchange information on mutual multicarrier capability in a registration procedure via registration request/response (AAI_REG-REQ/RSP) exchange with a base station.
As mentioned in the above description, in a system having multiple carriers supported by both a mobile station and a base station, a handover (HO) can be performed using multiple carriers. In this case, the handover means that a mobile station moves away from a radio interface of one base station into a radio interface of another base station. According to a general handover, a radio interface of one base station is switched to a radio interface of another base station using a single carrier. Yet, according to a handover in multicarrier environment, a radio interface is switched in a manner of preferentially performing a network reentry into a target base station using a primary carrier and then activating a secondary carrier. In doing so, the target base station exchanges information on a mobile station with a serving base station via a backbone network and is also able to transmit information on a secondary carrier to be preassigned to the corresponding mobile station (i.e., secondary carrier pre-assignment). Yet, when the target base station preassigns the secondary carrier to the mobile station, the secondary carrier is assigned with reference to mobile station information retained by the serving base station. However, if the serving base station and the target base station differ from each other in carrier configuration, it may cause a problem that optimal secondary carrier assignment is difficult.